1 Field of the Invention
The invention relates to a method of removing a photo-resist, and more particularly to a gradient elution method of removing photo-resist without moving to another region other than the current processing region.
2 Description of the Related Art
The process of fabricating an IC is very complex. Hundreds of steps are needed for making an IC. The fabrication normally takes one or two months to complete. The IC industry is a high technology industry including four main branches: IC design, wafer fabrication, wafer testing, and wafer packaging.
For example, the main purpose for the process of development is to clean the exposed part of photo-resist layer by chemical reaction, and to develop the transferred pattern.
There are many methods to perform a development process. For a commercial in-line operation, a "spray/puddle" method is normally adapted. The "spray/puddle" method comprises three steps. Firstly, developer is sprayed onto a wafer deposed on a spinner. Secondly, the wafer is puddle developed in a stationary status. Thirdly, after cleaning by water, the wafer is spun dry.
The next step after development is, before performing photolithography, to perform a quality control step, that is, an "after inspection (ADI)" step. The ADI step is to ensure the accuracy after the subsequent photolithography process. Thus, any abnormal state or condition can be found and reworked before the whole wafer is damaged in the subsequent process.
During photolithography, such as forming photo-resist, exposure, bake, or development, or before curing by ultra-violet and performing plasma bombardment, if a fault is found, the photo-resist has to be removed and reworked to avoid further damage. In the conventional semiconductor process, the process region of removing photo-resist and the processing region of photolithography are separate. Therefore, if a fault is found during fabrication, the photo-resist has to be removed in a region of removing photo-resist. The removal of photo-resist can not be performed in the processing region of photolithography, and thus, consumes a long fabricating time.
One of the conventional methods to remove photo-resist is to use an organic solution. The bonding of the photo-resist is destroyed by and dissolved in the organic solution. Normally, groups of acetone and aromatic base are used as the organic solution for removing photo-resist. In addition, photo-resist is an organic compound composed of carbon and hydrogen element. Therefore, an inorganic solution such as sulfuric acid (H.sub.2 SO.sub.4) and perhydrol (H.sub.2 O.sub.2), can be used to oxidise the carbon element into carbon dioxide (CO.sub.2) by perhydrol and to remove the hydrogen element by dehydration of sulfuric acid. Another method to remove photo-resist is by plasma.
Though several methods are available to remove photo-resist in a conventional process, almost all the removal regions of photo-resist are separated from the processing region of photo-lithography. Therefore, during processing, the faulty wafers have to be moved from the current processing region to the removal region of photo-resist for rework.